The present study was carried out to establish the larvicidal activities of crude and solvent extracts of Solanum nigrum L. leaves against Culex quinquefasciatus Say as target species. The results indicated that the mortality rates at 0.5% concentration were highest amongst all concentrations of the crude extracts tested against all the larval instars at 24, 48 and 72 h of exposure. Result of log probit analysis (at 95% confidence level) revealed that lethal concentration LC(50) and LC(90) values gradually decreased with the exposure periods in bioassay experiment with the crude plant extract. The results of regression analysis of crude extract of S. nigrum revealed that the mortality rate is positively correlated with the concentration of the extracts. Mature leaves of S. nigrum were also extracted with six different solvents [viz. petroleum ether, benzene, ethyl acetate, chloroform: methanol (1:1 v/v), acetone and absolute alcohol] to determine the best extractant for subsequent isolation and characterization of active ingredient. Mortality rate with ethyl acetate extract was significantly higher (p < 0.05) than other extracts when 50-ppm doses were used. The corresponding LC(50) value of acetone, absolute alcohol, petroleum ether, chloroform: methanol (1:1 v/v), benzene and ethyl acetate extracts were 72.91 ppm, 59.81 ppm, 54.11 ppm, 32.69 ppm, 27.95 ppm and 17.04 ppm, respectively, after 24 h of exposure period. Results of this study show that the ethyl acetate extract of S. nigrum may be considered as a potent source of a mosquito larvicidal agent.
The methanol leaf extracts of Glochidion neilgherrense, Cinnamomum wightii and Leucas linifolia are highly toxic even at low doses proven to be useful for larvicidal, pupicidal and adulticidal activity against Culex quinquefasciatus. The extraction of Glochidion neilgherrense, Cinnamomum wightii and Leucas linifolia are dose dependent and the mortality of the larvae increases as the doses of the sample were increased. Among all the instars, the fourth instar larvae were less susceptible to the plant extracts than first instar larvae. The mortality caused by some neural and muscular disturbance by the presence of variety of active compounds such as cytotoxic diterperiods, lactones and flavonoids in the plants. It was observed that the increase in concentration of extracts increased the potential activity of biocides against Culex quinquefasciatus. The decrease in egg hatchability was found to be dose dependent. There was increase in the larval-pupal duration, developmental duration, decrease in fecundity and egg hatchability, biting deterrency, in our study. The extract showed ovipositional deterrence and effective repellence against Culex quinquefasciatus at different concentration, with the observation on that maximal egg were laid in lower concentration of the extract and control. In oviposition deterrent and gravid mortality assay, the OAI values also indicated that the gravid and oviposited females were repelled by extracts and the reduced oviposition was due to the greater mortality of adults before they oviposited, caused by treatment of plant extract which contained of variety of active compounds. All the concentration of plant extracts hared promising mosquito repellency properties when tested against the adult mosquitoes of Culex quinquefasciatus. In the biting deterrency results, increasing in the concentration of plant extracts from 1% to 4% was found to increase the biting deterrency percentage.
Background Vector control is facing a menace due to the appearance of resistance to synthetic insecticides. Insecticides of plant origin may provide appropriate substitute biocontrol techniques in the future. The present study was carried out to investigate the bio control potentiality of active ingredient isolated from chloroform: methanol (1:1 v/v) extract of mature leaves of Solanum nigrum L. (Solanaceae) against early 3rd instar larvae of Culex vishnui group (comprising of Cx. vishnui Theobald, Cx. pseudovishnui Colless and Cx. tritaeniorhynchus Giles) and Anopheles subpictus Grassi. S. nigrum is a common plant distributed in many parts of India with medicinal properties.Methods Bioactive compound isolated from chloroform: methanol (1:1 v/v) extract of mature leaves of S. nigrum was (25, 45, 60 mg/L) tested against early 3rd instar larvae of Cx. vishnui group and An. subpictus. The lethal concentration was determined by log probit analysis. The chemical nature of the active substance was also evaluated following gas chromatography–mass spectroscopy (GC–MS) and infrared (IR) analysis. The compound was also studied on non target organisms such as Daphnia sp. and Diplonychus annulatum.ResultsTLC spot having Rf value of 0.94 (Rf = 14.1/15 = 0.94) showed larvicidal activity. In a 72 h bioassay experiment, mortality rate at 60 mg/L was significantly higher (P < 0.05) than those at 25 and 45 mg/L against early 3rd instar. Result of log-probit analysis (at 95% confidence level) revealed that LC50 and LC90 values gradually decreased with the exposure period showing the lowest value at 72 h of exposure. A clear dose-dependent mortality was observed, as the rate of mortality (Y) was positively correlated with the concentration (X) having regression coefficient value close to one in each case. The compound was found to be eco-friendly as it did not show any adverse effect to the studied non target organisms. Chemical characterization (GC–MS and IR analyses) of the active ingredient revealed the presence of phytosteroid compounds responsible for mosquito larvicidal activity.ConclusionLeaf extract of S. nigrum has great potential as bio control agent against Cx. vishnui group and An. subpictus. In near future the isolated bioactive phytochemical could be used as a source of an effective mosquitocidal agent.
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